Process for the methylation of vegetable oil soapstocks



3,010,977 PROCESS FOR THE METHYLATION F VEGETABLE 01L SOAPSTOCKS Paul H.Eaves, Metairie, and James .l. Spadaro, New Orleans, La., assignors tothe United States of America as represented by the Secretary ofAgriculture No Drawing. Filed Jan. 14, 1959, Ser. No. 786,897 1 Claim.(Cl. 260-4103) (Granted under Title 35, US. Code (1952), see. 266) Anon-exclusive, irrevocable, royalty-free license in the invention hereindescribed, throughout the world for all purposes of the United StatesGovernment, with the power to grant sublicenses for such purposes, ishereby granted to the Government of the United States of America.

This invention relates to the methylation of vegetable oil soapstocks.More particularly, the invention pro vides a commercially feasibleprocess for the methylation 'of acidulated vegetable oil soapstocks toimprove their properties, value, and utility. Vegetable oil soapstocksor foots are the mixtures of soap, entrained vegetable oil and aqueousliquid which are removed from crude vegetable oils in the course of analkaline refining of the oil. Raw foots are the semi-solid untreatedmixtures, in the form in which they are produced. Raw foots usuallycontain about 35 to 50% by weight of vegetable oil fatty acids, in theform of their alkali metal salts and as neutral oil, and about 50% byweight of water. Acidulated foots are the black oily liquids-produced bytreating raw foots with a mineral acid, to release the fatty acids, thenisolating the resulting organic phase consisting predominantly of fattyacids and neutral oil. Acidulated foots usually contain from about 85 to95% fatty acids. Hydrclyzed foots is a type of acidulated foots producedby treating the acidulated foots according to the Well-known Twitchellprocess or other processes which convert the neutral oil present to freefatty acids. Vegetable oil soapstocks are normally in surplus supply andof low cost. They are relatively unstable materials unles they receivespecial treatment, and are difficult to dispose of.

A primary object of the present invention is to provide a process ofmethylating the acidulated vegetable oil soapstocks to convert them to astable and more valuable and useful product. A further object of thepresent invention is to provide an efficient methylation process wherebythe major portion of the total fatty acids of the soapstocks areconverted to methyl esters, and the resulting methylated soapstockproduct possesses more desirable physical and chemical characteristics.

The generally practiced method in the prior art for preparing methylesters from free fatty acids or fatty materials containing free fattyacids consists of boiling under total reflux for from about 3 to 4 hoursa mixture comprising approximately 1 part by weight of the fattymaterial, 4 parts by weight of methyl alcohol, and 3 to 5% by weight ofa mineral acid catalyst based on Weight of fatty material. Under thesereaction conditions, a maximum of only approximately 80% of the fattyacids present can usually be converted to the. methyl esters. Using theprocess of the present invention, it has been found possible to shortenthe reaction time to as little as minutes, to reduce the proportion ofmethyl alcohol required in the reaction mixture, and to increase thepercent conversion of the fatty acids to methyl esters to about 90% orgreater.

In general, in accordance with the present invention, acidulatedvegetable oil soapstocks or hydrolyzed vegetable oil soapstocks aremethylated by heating said soap stocks at elevated temperatures underpressure with an Patented Nov. 28, 1961 excess of methyl alcohol in thepresence of an acidic catalyst. Substantially any acidulated orhydrolyzed edible vegetable oil soapstock produced by the conventionalalkali or soda ash. refining processes can be employed in the process ofthis invention. Suitable soaps-tocks include those from cottonseed oil,soy-bean oil, peanut oil, corn oil and the like.

The methylation treatment is preferably car-tied out at a temperatureand pressure high enough to maintain the methyl alcohol in the liquidstate and to make possible an elficient methylation in a short reactiontime. For example, at temperatures of and C. pressures of about 40 and80 p.s.i.-g., respectively, are theoretically required to maintain themethyl alcohol in the liquid state. In practice, a safety factor isusually provided for. Accordingly, it is generally preferred in theprocess of the invention to employ a temperature of from about 100 C. toabout C. and a pressure of from about 120 to 180 p.s.i.g. A temperatureof 120 C. and a pressure of p.s.i.g. are particularly preferred. Underthese conditions, only a short reaction time, usually about 10 to 15minutes, is required for maximum conversion of the fatty acids to methylesters. The reaction time is critical in that if it is too brief themaximum conversion of total fatty acids to methyl esters is notachieved, and if it is too long there is danger of degradation of thefatty acids. In the preferred practice, the reaction is generallycarried out for from about 10 to 15 minutes. Reaction times in excess ofabout 20 minutes are not usually neces sary or desirable.

Acidic catalysts are preferred for use in the process of the inventionbecause of their tolerance for small amounts of water such as are foundin most acidulated soapstocks. Mineral acid catalysts such as hydrogenchloride or sulfuric acid can be employed. However, the preferredcatalyst is a Twitchell-type catalyst in an excess of sulfuric acid.This catalyst is prepared by reacting one mole of naphthalene, benzene,or similar cyclic hydrocarbon with one mole of mixed, long chain (predominantly C or greater) fatty acids and six moles of 100% sulfuricacid. When naphthalene is employed, the product of the said reaction isessentially an anhydrous mixture of fatty acid naphthalenesulfonic acidsand excess sulfuric acid which is used as the catalyst without furtherpurification. The sulfuric acid is probably the major catalytic agentpresent with its activity enhanced by the emulsifying action of thefatty acid naphthalenesulfonic acids. From about 1 to 5% by weight ofthe catalyst, based on the weight of total fatty acids in thesoapstocks, is generally preferred for the methylation reaction of theprocess of this invention. A particularly suitable amount of catalyst touse is 3%. It is usually convenient to dissolve the catalyst in methylalcohol prior to adding it to the reaction mixture.

It is preferred to employ a homogeneous reaction mixture for themethylation. Therefore, a sufficient excess of methanol to give completesolution of the soapstocks being methylated is desirable. It has beenfound that this can be achieved by using approximately 5 moles of methylalcohol for each mole of total fatty acids in the soapstocks. Thispreferred ratio of reactants is equivalent to approximately 35% methylalcohol and 65% soapstocks by weight which is a considerably lowerproportion of methyl alcohol than used in conventional processes for themethylation of fatty materials. It provides an adequate amount of thealcohol for the complete methylation of the soapstocks and at the sametime is the lowest amount of alcohol giving essentially completesolution of the soapstocks. It is inefficient and uneconomical to use amuch larger excess of methyl alcohol than this. It is generallypreferred to employ absolute methyl alcohol, but up to approximately 2%by weight of water in the alcohol can be tolerated.

The methylation of the soapstocks is preferably carried out by acontinuous procedure employing any appar-atus capable of withstandingthe operating temperatures and pressures. A continuous reactor of thepacked column type, provided with an integral flash evaporator, isparticularly preferred. This type of reactor enables the operator toachieve precise control of reaction time, temperature, and pressure andmakes possible the use of short reaction times at elevated pressures andtemperatures. The operator can use either a single stage reactor or amultiple number of stages, with a single or multiple pass reaction inany stage. The desired extent of methyla'tion can usually be achieved ina single pass or double pass reaction. In view oft-he high pressures andshort reaction times employed for the methylation reaction, it is notgenerally desirable to use a batchwise procedure.

When employing a continuous reactor according to the preferred operatingprocedure in the process of the invention, centain conventionalauxiliary equipment is used. This auxiliary equipment comprises a feedsupply tank or other means for holding the proportioned mixture ofsoapstock, methanol, and catalyst; a high pressure variablerate positivedisplacement pump or other suitable device for pumping the reactantsthrough the packed column reactor; a pressure gauge and a variablepressure discharge valve or other means for indicating and maintainingthe desired operating pressure; a fiash evaporator and condenser, orother means for rapidly removing methanol and water at the end of thereaction period;

and suitable receiv-ing vessels for the distilled solvent and N for themethylated soapstock product.

In operation of the continuous reactor, the reaction temperature can beconvenientlycontro-lled by regulating the pressure of steam introducedinto a jacket surrounding the packed column reactor. The pressure in thereactor is controlled by means of the variable pressure discharge valve,and the time of retention of the material in the reactor by the rate offeed input to the reactor.

The preferred type of flash evaporator comprises a flash chambersupplemented by a falling film tube, both being heated by external steamcoils or other suitable means and operated under reduced pressure. Thehot material is discharged from the packed column reactor 'via thevariable pressure discharge valve into the evacuated ilash chamber wherethe major portion of the excess methanol and the water formed by thereaction are removed by flash evaporation. The remainder, if any, isevaporated from the material as it trieklesdown the falling film tubeattached to the flash chamber.

Flash evaporation serves two important purposes in "the process of thepresent invention. The first of these is to terminate the methylationreaction by almost instantaneous removal of unreaoted methanol and ofwater. The second is that the methylated soapstock product, being freeof methanol and water, is satisfactory for distillation or othersubsequent treatments or it can be used without further treatment. Forexample, it is possible to add fresh methanol to the product and repassthe mixtore through the reactor to increase the yield of esters. Thepercentage of fatty acids esterified can usually be increased by about5% or more as the result of a single repass operation under thepreferred conditions. the removal of unreacted methanol and water fromthe reaction mixture, the catalyst precipitates from the methylatedproduct and can be removed by mechanical means if the operator desires.However, the catalyst is not generally objectionable and can be left inthe methylated product.

The process of the present invention provides a convenient means ofproducing valuable methyl esters of fatty acids from a low cost fattymaterial, namely vegetable oil Soapsto-cks. When this'isthe primary aim,it

After a is preferred to employ hydrolyzed soapstocks as the startingmaterial, since essentially all the fatty acids therein are present asfree fatty acids, and carry out the methylation in a multiple stagereaction. Under these preferred conditions, about 96% or more of thefatty acids are converted to methyl esters which can be recovered by theconventional distillation procedures.

The methylated soapstocks produced according to the process of theinvention do not have the undesirable characteristics of the acidulatedor hydrolyzed soapstock's. In contrast to the latter which are solid atroom temperature and must be heated to render them liquid before theycan be pumped or sprayed, the methylated soapstocks remain liquid atroom temperature even in cold Weather and can be handled easily. Theyare low in free fatty acid content, highly resistant to oxidation,noncorrosive to iron and steel vessels and equipment, and do not tend tobecome rancid like the unmethylated soapstocks which contain a higherpercentage of free fatty acids.

Fatty materials are conventionally added to certain animal feeds in upto about 10% concentration by weight of the feed as a high caloricnutrient and anti-dusting component. The methylated soapstocks of thepresent invention are particularly suitable for this purpose as theypossess the previously described desirable chemical and physicalproperties in addition to being of high caloric value and having.anti-dusting properties. When added to a dry material, such as a feed,the methylated product is easily dispersed uniformly throughout thematerial Without forming lumps or balls and reduces the dustiness of thematerial. The stability and keeping qualities of the resulting mixtureare much superior than when unmethylated soapstocks are employed as theadditive.

The following examples are given by Way of illustration of the detailsof at least one method of practicing the invention, and are not by wayof limitation of the invention.

' Example 1 A sample of commercial grade acidulated cottonseed oilsoapstocks was used in these experiments. The acidulated Soapstockscontained 91.3% total fatty acids and 16% neutral oil.

Representative portions of the sample of acidulated soapstocks weremethylated for various periods of time in a. continuous, packed columntype reactor as previously described using a single pass reaction andthe following reaction conditions: temperature, C.;pressure, p.s.i.g.;Twitchell-type catalyst (prepared from naphthalene, mixed cottonseed oilfatty acids, and 100% sulfuric acid as described earlier), 3% by weightbased on Weight of total fatty acids (TFA) in the acidulated soapstocks;mole ratio of methyl alcohol to total fatty acids, 5 to l.

The effect of length of reaction time on the conversion of total fattyacids in the acidulated soapstocks to methyl esters is summarized in thefollowing table:

Percentage of input TFA recovered as methyl esters by distillationReaction time, minutes 5.1. 78. 4 1n n 81. 4 1a a 82. 4 19.7.- 83. 1 251 .s 81. 9

Example 2 The same lot of commercial grade acidulated cottonseed oilsoapstocks used in Example 1 was employed in these experiments.

Representative portions of the soapstock sample were methylated for 10minutes in the same apparatus and in exactly the same manner asdescribed in Example 1, except that varying amounts of theTwitchell-type catalyst were used. Experiments were also conducted inwhich the same methylated product was passed through the reactor twice(10 minutes reaction time for each pass), the initial 5 to 1 mole ratioof methyl alcohol to TFA being restored by adding the required quantityof fresh methyl alcohol to the alcoholand water-free methylated productfrom the first pass. No additional catalyst was used for the secondpass.

The effects of catalyst concentration and number of passes on theconversion of TFA in the acidulated soapstocks to methyl esters aresummarized in the following table:

Percentage of input 'IFA recovered as methyl esters Catalystconcentration, percent by by distillation weight based on weight of TFASingle pass Double pass reaction reaction Example 3 Percentage of inputTFA recovered as methyl esters Catalyst concentration, percent by bydistillation weight based on weight of TFA Single pass Double passreaction reaction Example 4 A dilferent lot of commercial gradeacidulated cottonseed oil soapstocks than that used in Examples 1 and 2was employed in this experiment. The acidulated soapstocks contained96.0% total fatty acids and 28.1% neutral oil.

The acidulated soapstocks were methylated for 10 min utes in the samemanner and under the same conditions as described in Example 1, exceptthat the reaction temperature varied between 114 C. and 123 C., being119- 121 C. for approximately of the reaction period.

Following removal of excess methanol and water by the usual flashevaporation procedure, the methylated product was filtered throughfilter paper. Material removed by filtration represented only 2.1% ofthe methylated product. The filtered methylated product contained 93.0%total fatty acids, and 87.7% methyl esters plus neutral oil. I It was adark brown to black oily liquid having a somewhat pleasant fruity odor.When incorporated into a standard poultry feed ration at the 5% and 10%fat levels and fed to poultry over a 10 Week period, it gave resultsequivalent to those obtained using a conventional fat additive(stabilized white grease) at comparable fat levels. LD value in excessof 40 cc./ kilogram.

We claim:

A process for producing methylated vegetable oil soapstocks fromacidulated vegetable oil soapstocks comprising the following steps;heating a homogeneous reacting mixture of vegetable oil soapstocks inmethyl alcohol solution for from about 10 to about 20 minutes at atemperature of from about C. to about 125 C. and at a pressure at leastsuflicient to maintain the methyl alcohol in the liquid state, in thepresence of about from 1 to 5% by weight of a Twitchell-type catalystbased on the weight of total fatty acids in said acidulated soapstocks,at least about 5 moles of methyl alcohol being used for each mole oftotal fatty acids present in said acidulated soapstocks; andflash-evaporating the unreacted methanol and the water from the reactionmixture,

References Cited in the file of this patent UNITED STATES PATENTS1,659,790 Starrels Feb. 21, 192.8 2,486,938 Fish Nov. 1, 1949 2,876,242Thurman Mar. 3, 1959 It was nontoxic to chicks and had an i

